327 receiver calibration.
The 327 Mhz receiver is a dual linear receiver
with room temperature amplifiers and a 30 Mhz wide filter.
Sections:
History
Recent
system performance measurements
Daily monitoring of tsys.
Calibration measurements
rfi
cal
values
rfi measurements
all measurements in date order
haslam
et
al
408
Mhz all sky survey (.pdf) .. 18.9 Mb
327 rcvr block diagram (.pdf)
- This is an older diagram with the room temperature receiver.
327 filter bank (.pdf)
Hybrid between antenna and filters (aug14)
(.jpg)
History:
11may20:
polA stage 2 bias glitches cause glitches in signal (it's been
there awhile)
26sep14: hybrid reinstalled.. back to circular.
08aug14: hybrid removed .. alex W. wanted linears.
13jan13: updated pointing offset
06jun11: hybrid installed on antenna.
04jan10: Now cooling is on one of the alfa compressors.
13jun08: Cooled 327 receiver installed. New cal values also
installed.
13apr06: rf cable of channel A between the front end and
the filter at the post amp was replaced because it was bad. The
cal cable for channel B between the postamp chassis and the
antenna was also replaced.
11apr06: 750 Khz comb appeared. 39.45 Khz comb was seen (but
not sure when it appeared). Turned out to be the sband
cabinet in dome.
07jan04: 327 receiver moved to a new position on the turret
floor (to make room for alfa).
jul02: room temperature receiver installed.
11jul02: cal values measured in lab.
Calibration
measurements: (top)
13jan13:
calibration results: jun12-dec12. updated pointing offset.
21jun08: SEFDA/SEFDB shows that tsys polB
is 10% larger than tsysB.
feb05: gain curves for data
taken mar03 to feb05 (GAIN CURVE)
feb05: system performance
for gain curve data mar03-feb05
08aug02: Calon/off sky
and load. Tsys contributions receiver, sky
07aug02: calibration runs
3C138,B0640+233, and B08224+294
20mar14:
drifting birdie 320->325.. cal control cards
feb14:
p1693 pulsar search data taken during the cable repair
10aug11: short
duration broadband rfi seen by p2558 in 327 rcvr.
09aug09: rfi
from azimuth encoders
Cleaning
up
the
327
Mhz band (last updated 03nov05):
05nov05:
azimuth
dependence
of
birdies in the 327 rcvr.
21oct05:
output
of
327Mhz
rcvr after the 1st amp (and before the rf filter).
16oct05:
1
Mhz
comb
coming from dome AC units.
27aug05:
the
16Khz
comb
in the 327 rcvr comes from the alfa motor controller.
All measurements in date
order (top)
11may20:lna polA stage 2
current glitches seen in ips data.
20mar14:
drifting birdie 320->325.. cal control cards
feb14:
p1693 pulsar search data taken during the cable repair
20feb14:
total power dropouts seen in p1693 data.
26jun13:
P2717 327 incoherent search with puppi show avg spectra, rms, and
rfi.
13jan13:
calibration results: jun12-dec12. updated pointing offset.
20apr12: bandpass shape of cavity filter in front
of dewar.
10aug11:
short
duration
broadband rfi seen by p2558 in 327 rcvr.
09mar11:
az dependence of 327 rfi
13dec10: tsys vs ra,dec and
l,b 09may09 thru 13dec10
09feb10: p1693 drift scan 220 sec dynamic
spectra and spectral avgs.
09aug09: rfi
from azimuth encoders
07may09: tsys vs sky position for jun2008 to
may09
16jul08: tsys vs date,hr,ra,dec with cold
receiver
21jun08:
SEFDA/SEFDB
shows
that
tsys polB is 10% larger than tsysB.
07may07: Strong 60 Hz in p1693 pulsar
data using the 327 receiver and the wapps.
05nov05:
azimuth dependence of birdies in the 327 rcvr.
03nov05: Cleaning up the 327 Mhz
band (last updated 03nov05):
21oct05: output
of 327Mhz rcvr after the 1st amp (and before the rf filter).
16oct05: 1 Mhz comb
coming from dome AC units.
27aug05: the
16Khz comb in the 327 rcvr comes from the alfa motor controller.
feb05: gain
curves for data taken mar03 to feb05 (GAIN CURVE)
feb05: system
performance for gain curve data mar03-feb05
08aug02:
Calon/off sky and load. Tsys contributions receiver, sky
07aug02:
calibration runs 3C138,B0640+233, and B08224+294
jul02
:Room
temperature
receiver
installed
07jan04: 327
receiver moved to new turret position.
29sep00:Turret
posit
A noise source was injected into the cavity filter
before the dewar to measure the filter shape. The setup was:
- noise injected into one pol of the cavity filter. This
is after the polarizer so we were in linear mode.
- The iflo was setup for 750 IF (wideband)
- The 30 Mhz RF filter was not used
- The mock spectrometer took data with a 172 Mhz bandwidth
centered at 327 Mhz
- I normalized the plots to the median value of 10 Mhz about 327
(but excluding 326-238)..
The plots show the cavity
filter shape (.ps) (.pdf):
- The black line is polA. The red line is polB
- Top: bandpass shapes: linear scale
- Bottom: bandpass shapes: dbscale.
Summary:
- the center freq of the filters is 325.5
- The fwhm of the filters is: 71 (polA), 65 (polB) Mhz.
- The decrease in rolloff at the edges may be power aliased back
in by the sampling.
- When users select the 750 Narrow Band IF, a 60Mhz filter is
installed. They won't see thee 65 or 71Mhz bandwidths.
processing:
x101/120420/327_filter.pro
09feb10:p1693 drift scan:
p1693 did a long drift scan using the wapps on
09feb10. The setup was:
- cfr: 327, bandwidth: 50Mhz, 3lvl sampling, 200Usec dumps,
addpols
- az,za:275,15.49
The first file of data was looked at (about 2 minutes)
dynamic spectra for 2 minutes of
data (.gif):
- spectra were hanning smoothed and averged to .5 seconds.
plots of the average spectra and the
rms/mean (.ps) (.pdf):
- Top: the 220 second average spectra. The vertical scale is
linear in power.
- Bottom: the rms/mean by channel for the first File. The rms
was computed after averging to .5 seconds.
- The expected rms (from the radiometer equation) is show in
red.
processing:
x101/100209/p1693drift.pro
07may09: Tsys vs ra/dec and Tsys vs
galLong/galLat. (top)
Tsys data from 13jun08 (start of 327 cooled
receiver) thru 07may09 was plotted vs ra,dec and galactic l/b to
show the portion of Tsys that is coming from the sky. Only data with
zenith angle below 15 degrees was used (to not include the tsys za
variation).
PolA plott
Tsys
vs
sky
position
(.ps) (.pdf):
- PolA is plotted in black
- PolB is
plotted in red
- Page 1: tsys vs ra,dec
- Top: ra,dec positions where the measurements were made.
- We normally sit at az=270,or 285 and za=around 10.
- Center: Tsys vs Ra.
- Places with elevated Tsys
- ra=6 galactic anticenter
- ra=15-17 north polar spur
- ra=19 : galactic plane
- Bottom: Tsys vs Declination
- Not much info since most decs are 15 or 18 Deg.
- Page 2: tsys vs galactic longitude
and latitude.
- Top: galactic latitude and longitude for the measurements
- Center: Tsys vs gal Longitude
- Places with elevated Tsys
- long=35 North polar spur
- long=50 galactic plane
- long=190 anticenter
- Bottom: Tsys vs galactic latitude
- lat -5 anticenter
- lat=5 galactic plane
- lat 30-70 top set, north polar spur
- Page 3: TsysB - TsysA vs ra,
galactic latitude
- The top plot is vs Ra, the bottom plot is versus galactic
longitude.
- There is not a lot of structure vs ra or longitude.
Polarization is probably not playing a major part.
- The median value is 8.9 Kelvins with an rms of about 5K
Summary:
- The lowest Tsys for polA was about 85 K around ra=9-12 hrs
- Tsys can increase to > 160 K on the plane
- PolB is 8.9K warmer than polA.
Processing:
x101/090506/tsysplotradec.pro
16jul08: tsys vs date,hr,ra,dec with
cold receiver (top)
The tsys measurements from 14jun08 to
16jul08 were used to plot tsys vs various parameters to see why tsys
was sometimes high.
The plots show Tsys vs date, hr, ra,
dec, za (.ps) (.pdf):
The black * are polA while the red * are polB. Tsys for polB is about 10K higher than
polA.
- Top: tsys vs date.
- 2nd: tsys vs Hour of day.
- tsys before 10 am seems to be higher than than after
10am. Could it be sunrise??
- 3rd: tsys vs za. we usually do tsys around za=10.
- 4th: tsys vs ra.
- The high points at ra=15 are the north polar spur. At 408MHz
it is about 20K higher than the ra=10 data (327 will be
higher).
- The points at 2-4 hours with tsys =100 do not have a lot of
continuum. These are the 7-10am points in plot 2.
- 5th: tsys vs dec. Most points are taken between decs of 15-20
degs..
- The high point at dec=2 corresponds to ra=15. The continuum
here is not that large (the north polar spur picks up at
ra=15, dec=10-20) So i'm not sure why this is so high.
SUMMARY:
- Tsys can vary by 20-30 kelvins with sky position
- 8am-10am seems to be higher than 12-19 pm.
21jun08: Ratio SEFDA/SEFDB shows
Tsys B > TsysA (top)
The tsys measurements
after the cooled receiver was installed on 13jun08 showed that Tsys
PolB is about 10K higher than Tsys polA. To see if this was a
cal problem or a real Tsys difference, calibration scans using the
source B0316+162 (CTA21) were done and then the SEFD ratio was
computed. The setup and processing was:
- source CTA21 is unpolarized
- 03 hours is far enough away from the north polar spur that the
background should not be polarized.
- Bandwidths of 25, 1.5, .78 Mhz were measured all centered at
326 Mhz.
- SEFD=Tsys/Gain or SEFDA/SEFDB = (TsysA/TsysB)*(GainB/GainA)
- since both Tsys and Gain depend linearly on the cal, the cal
is cancelled by the ratio. The sefd is not affected by errors in
the cal
The plots show the calibration
measurement results (.ps) (.pdf):
- Top: TsysA and TsysB vs za.
- TsysB is 10 to 15 Kelvins higher than TsysA
- The 25 Mhz band of polb is about 5K higher than the 1.5 and
.78 Mhz bandwidths. This may partly come from using the cal
value at the center of the band for the entire band.
- Middle: Tsource A and T source B.
- PolA and polB both give close to the same source
temperatures so the cal values are not wrong by much.
- PolB gives the same source temperature for all of the
bandwidths so using the cal value at 326 MHz is not the reason
why the top plot showed a difference in the polB bandwidths.
- Bottom: SEFDA/SEFDB
- The ratio is 90 to 93% so TsysB is really higher than TsysA.
Conclusion:
- Tsys polB is about 10% higher than Tsys polA.
- Tsys (measured at 326Mhz) for polB 25 Mhz is about 5%
higher than Tsys measured with 1.5 or .78Mhz bandwidths
processing: x101/080621/chk327.pro
28feb05: gain curve for
data taken mar03 to feb05 (top)
Calibration data taken march03 to feb05 was used
to fit a gain curve for the 327 receiver (the data was taken
at 326 Mhz). For the data to be included in the fit, it had to
satisfy the following constraints:
- 6 < gain < 11.5 K/Jy
- Sefd < 18
- average beam width between 800 and 950 arc seconds.
These constraints were used to remove some bad measurements. The cal
values used were those measured in the lab in jul02 (see the system
performance for gain curve data for a more complete description).
Gain curves were then computed fitting for gain
as a function of za. The fitting function (with za in degrees) is:
g(za)=c0 +c1*za + c2*(za-14)^2
+c3*(za-14)^3
where the ^2 and ^3 terms are only applied for za ge 14 degrees.
The plots show the gain
curve
and
the
residuals (.ps) (.pdf):
- Fig 1: the azimuth , za coverage for the data.
- Fig 2 top: Red is the data, black is the fits. The fit
coefficients are listed on the plot. The fit rms is .47 K/Jy.
- Fig 2 bottom: The fit residuals. The colors are different
sources.
The source with low flux (red x ) i s B0320+053. Its flux may be a
bit off. At 1400 Mhz our flux differs from nvss by about 8%. The
yellow diamonds that are high come from B0521+281. The cal values
for the 327 receiver have jumped around by up to 10 kelvins in
the last two years (see 327
Mhz tsys difference 2004,2003). If the polA-polB
jump was do to a shift in the cal, then it will affect any
calibration data taken during these jumps (i guess i need to check
this out..)
The fit coef can be found in the ao idl
distribution in the file data/gain.datR1. At AO it is found in the
file /share/rsi/local/libao/phil/data/gain.datR1.
processsing: x101/327/feb05/dogaintfit.pro
28feb05: system
performance for gain curve data mar03-feb05 (top)
Calibration data taken mar03 to feb05 was used to
fit gain curves for the 327 receiver. For the data to be included in
the fit, it had to satisfy the following constraints:
- 6 < gain < 11.5 K/Jy
- Sefd < 18
- average beam width between 800 and 950 arc seconds.
These constraints were used to remove some bad measurements. The cal
values used were those measured in the lab in jul02. The plots show
the
system performance for the gain curve data (.ps) (.pdf)
:
- Fig 1 top: the az, za coverage for the data
- Fig 1 bottom: the time of day when the data was taken
- Fig 2: gain, tsys, sefd, and average beam width. B0640+233 had
a beam width that was larger than normal. It tended to make the
gain a little less.
- Fig 3: coma, avg first sidelobe, eta main beam, eta main beam
+ first sidelobe.
- Fig 4: pointing error: za vs za, za vs az, az vs za, az vs az.
The large az error for B0017+154 was after the horn had been
moved and before the final turret offset had been computed. This
is purely an az offset and did not affect the gain. Some of the
other az,za pointing offsets were probably from tilts (rain
etc..) that would also affect the gain.
processing: x101/327/feb05/doit.pro
07jan04: 327 receiver
moved to new turret position. (top)
The 327 receiver was moved on 07jan04 from turret
position 21.5 to turret position 340. This was done to make room for
the alfa receiver. Calibration scan data was taken on 05,06jan04
before the move and on 07jan04 after the move. The goal is to make
the average pointing error before and after the moves the
same. The az error can be manipulated by changing the turret
position, the za error can only be modified by moving the feed.
The pointing
error
before and after the move is shown in the plots.
- Fig 1 has the pointing error in great circle arc seconds vs
azimuth and za. The black color is before the move with the
turret at 21.5 degrees. The green color is after the move with
the turret at 340.2 degrees.
The za pointing error remained within 1 arc second. The azimuth
pointing error for source 2 on the second day (green) varied with za
(tiedown losing tension??). To compute the mean (actually median
values) I only used source 1.
|
medianAzErr
asecs |
medianZaErr
asecs |
| before move(tur=21.5) |
-11.73 |
-17.05 |
| after move (tur=340.2) |
-26.84 |
-16.39 |
The average az error with the turret at 340.2 degrees is
(-11.73-(-26.84))=15.1 asecs too small. We need to move the
azimuth by +15.1 asecs. The turret coordinate system is opposite
to the azimuth and 1 turret degree equals 45 arc seconds on the
sky. The turret needs to be moved to 340.2-(15.1/45)=339.9 This
will be the new turret position.
08aug02:calOn/off load
and sky. Tsys contributions receiver, sky. (top)
30 cal on offs were done while the load switch
was on , and 30 more calon/offs were done while tracking blank sky
(ra:075055, dec:240000). The telescope was centered at 327 Mhz and
25,12.5,6.25, and 3.125 bands were used. 2 seconds cal on were
followed by 2 seconds cal off. The cal values used were: 73.2 pola,
76.1 polB.
The load is beneath the rotary floor close to the
antenna. The temperatures were: room:92, platform:85, tertiary
platform:92 (this was after an sband radar run). Remeasuring these
values 20 minutes later, the temperatures were all within 1 F of the
original values. Using an ambient temperature of 90F gives a load
temperature of 305K.
The plots show the
system temperature measured for the cal on/offs. The lines are
calOff, the * are cal on. PolA is black while polB is red.
- Top: Cal on,off using the load.
- Bottom: Cal on,off tracking blank sky.
On load calOff the average temp was 375K.
Using 305K for the ambient load temperature gives a noise
contribution from after the load of 375K-305K=70K for a noise
contribution after the load switch. This is what is expected for
the room temperature amplifier.
On sky calOff the average temp was 135K. This
includes the flange temperature, sky temperature, and any
ground/scattered/spillover radiation. Using 40K for the sky
contribution and 70K for the flange temperature gives 25K from the
spillover/scattered ground radiation. Higher frequency receivers
have shown scattered radiation ranging from 10 to 20 K so 25K for
the 327 receiver seems reasonable.
The sky temp was crosschecked with chris
salters 408 Mhz survey and it came out to 39.1K.
327 Tsys budget
| load temp |
305K |
| receiver temp |
70K |
| Tsys on sky |
135K |
| sky temp |
40K |
| spillover,scattered radiation |
25K |
processing: x101/020808/docal.pro
07aug02: calibration runs
3C138,B0640+233, and B0824+294 (top)
Calibration runs using the heiles scan were done
on 3C138 (B0518+165), B0640+233, and B0824+294 during the day. The
first two sources were done after transit, while the last
(B0825+294) covered 2 strips before transit until set.
B0640+233 has a width of 72" by 17" at lband while the other
two sources are < 16". The field has other sources within
the +/-3 beams that were on the order of 3% of the source. The plots
show the calibration results:
Fig 1. has gain Kelvins/Jy, Tsys, Sefd, and average beam width.
The za dependence of the gain and tsys look correct. The gain is
about 11 K/Jy, Tsys about 150 K, SEFD 14, average beam width: 14
Amin
Fig 2 shows the coma parameter, first sidelobe height: -14 db,
main beam efficiency 65% (using 3C138), and main beam + first
sidelobe efficiency of 80% (using 3C138)
Fig 3 has the pointing errors for these runs. Most of the data
was taken after transit so the pointing errors may be biased to
one part of the dish. The mean za Error is -142 Asecs with
an rms of 34 Asecs. The feed is pointing too far downhill. The
mean azimuth error is -3 Asecs with an rms of 24 Asecs. This feed
was not surveyed into position. The mean pointing error can be
fixed by updating the model for 327. (Note: updated pointing model
07aug02).
measured 327 performance
| gain |
11 K/Jy |
| Tsys |
150 K |
| sefd |
14 Jy/Tsys |
| avgBeamWidth |
14 Amin |
| First sidelobe |
-14 db below peak |
| mainBeamEffciency |
65% |
processing: x101/020807/doit.pro
jul02 Room
temperature receiver installed
The 327 receiver had been removed in 2001 to be
worked on. It was re-installed in jul02 with a room temperature
receiver.
29sep00: Turret Position:
The 327 system was installed in late september under the turret
floor. For a number of receivers we have found a local maximum in
the system temperature when the turret is aligned with the optic
axis. I did a number of turret scans on blank sky to find the turret
position of this local maxima.
setup:
On 29sep00 the turret was driven in a sine wave about turret=22
degrees with an 8 degree amplitude and 15 second period. The
telescope was parked at az=270, za=10. 2 polarizations were
recorded. Each was detected with a .02 sec time constant.
The turret
strips
figure shows the average of 8 minutes of data tsys versus
turret position. The top plot is polA and the bottom plot is polB.
The units are a/d counts with the average value as the system
temperature. The local maxima occurs at 24.5 deg (polA) and
17.5 deg (polB). The turret scale factor is 45 arcsecs (great
circle) per turret degree. If the difference is caused by a
misalignment of the dipoles then it is about 5.25 arcminutes or 1/3
of a beam. We need to do some scans on a continuum source to verify
that this is beam squint.
processing: x101/000929/chkpnt.pro
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